The present invention relates to a diaphragm pump that includes a plurality of diaphragms in a housing.
A diaphragm pump generally includes a diaphragm for defining a pump chamber in a housing and a drive mechanism for deforming the diaphragm thereby to vary the volume of the pump chamber. According to the variation of the volume of the pump chamber, the pump performs a pumping action, drawing therein and discharging therefrom a fluid. In a diaphragm pump with a mechanical drive mechanism (a mechanical type diaphragm pump), when the difference between the pressure in the pump chamber and the atmospheric pressure is increased, the diaphragm may be damaged due to the increased pressure difference. Thus, it is difficult to set the discharge pressure of the mechanical type diaphragm pump at a high pressure value.
According to prior art disclosed in Japanese Patent Application Publication No. 53-41803, the discharge pressure of the mechanical type diaphragm pump is set at a high pressure value. More specifically, a plurality of pumps is provided, and the fluid discharged from the former pump is drawn into the subsequent pump, thereby raising the pressure of the discharged fluid in stages. As a result, a desired high pressure in the fluid discharged from the last pump is obtained. In this prior art, in order to suppress the pressure difference that is applied to the diaphragm, a sealed chamber is provided for accommodating each diaphragm pump, and the fluid subjected to pressurization is made to stay in the sealed chamber and then is drawn into the pump.
As to another prior art, the diaphragm pump disclosed in Japanese Patent Application Publication No. 2000-136775 is known. The diaphragm pump includes two diaphragms. A pressure chamber (or a pump chamber) is defined in the housing by one of the diaphragms, and a pressure control chamber is defined between both of the diaphragms. A passage is provided for connecting the pressure chamber to the pressure control chamber, and a check valve is disposed in this passage. According to this prior art, the reversal of the diaphragm is prevented during operation of the pump by constantly adjusting the pressure in the pressure control chamber to the negative or positive pressure with respect to the pressure in the pressure chamber.
In the art of Japanese Patent Application Publication No. 53-41803, the back pressure on the diaphragm correspond to the discharge pressure of the former diaphragm pump. When the difference between the discharge pressure and the suction pressure (or the discharge pressure of the former diaphragm pump) is great, the diaphragm may be damaged due to the great pressure difference. In the diaphragm pump of such type, therefore, a compression rate needs to be set based on the suction pressure (or the discharge pressure of the former diaphragm pump). Since the fluid discharged from the former diaphragm pump is drawn into the subsequent diaphragm pump, the discharge pressure of the subsequent diaphragm pump may be insufficient depending on timing of operation of the former diaphragm pump.
In the art of Japanese Patent Application Publication No. 2000-136775, two diaphragms are provided in the housing of the pump. When the pressure in the pressure control chamber is adjusted to the positive pressure with respect to the pressure in the pressure chamber, the fluid in the pressure chamber having the discharge pressure is introduced into the pressure control chamber. The fluid having the discharge pressure which has been introduced in the pressure control chamber does not flow out therefrom due to the check valve. Thus, the pressure in the pressure control chamber is maintained at the discharge pressure. This creates a resistance against the deformation of the diaphragm so that there is a fear that the fluid may be prevented from being drawn into the pressure chamber. In this regard, the pressure in the pressure control chamber is substantially the same as that in the pressure chamber when the pump discharges therefrom the fluid, so that no pressure difference is applied to the diaphragm. However, when the pump draws therein the fluid, the difference between the pressure in the pressure control chamber and the suction pressure in the control pressure is significantly great. This great pressure difference may increase a load on the diaphragm adjacent to the pressure chamber. Japanese Patent Application Publication No. 2000-136775 further discloses an embodiment in which the pressure in the pressure control chamber is adjusted to the negative pressure with respect to the pressure in the control chamber. In this case, no fluid is introduced from the pressure chamber into the pressure control chamber due to the check valve, and the pressure in the pressure control chamber is substantially the same as the suction pressure. When the difference between the discharge pressure and the suction pressure is great, the diaphragm may be damaged due to the great pressure difference similarly to Japanese Patent Application Publication No. 53-41803.
The present invention is directed to a diaphragm pump that achieves high discharge pressure and reduces the load on the diaphragm caused by pressure difference.